1. Field of the Invention
The present invention relates to μ-law and A-law which are respectively an international standard for PCM digital transmission of telephonic speech, particularly relates to μ-law-to-A-law translating equipment and A-law-to-μ-law translating equipment.
2. Description of the Related Prior Art
For a PCM telephone line, there are a line encoded according to μ-law and a line encoded according to A-law based upon ITU-T Rec. G. 711. μ-law is used in Japan and North America and A-law is used in European countries. Therefore, in case an international PCM telephone line is laid between two countries different in a conversion law, a PCM speech signal is required to be converted to a different conversion law in a connection between communication networks of both countries. For this conversion, a μ-law-to-A-law converter and an A-law-to-μ-law converter are used. For example, a μ-law-to-A-law converter or an A-law-to-μ-law converter is provided every line to a primary PCM telephone line of 1.544 Mbits/s or 2.048 Mbits/s. In case the number of lines is increased, these converters are required to be also increased by the same number as the number of lines. However, when the μ-law-to-A-law converter or the A-law-to-μ-law converter is increased, the cost is increased and the reliability is deteriorated.